Electrical circuit for fluorescent lamps

ABSTRACT

A portable fluorescent task lamp comprising at least two fluorescent bulbs of any wattage up to forty Watts and of either a non-starting type or a self-starting type; and an electronic ballast circuit for use therewith including an SPST function switch disposed in series with each fluorescent bulb, wherein the fluorescent bulbs may be ignited and sustained in illumination in parallel, simultaneously or individually, as determined by the respective SPST switches.

CROSS REFERENCE TO RELATED APPLICATIONS

The present U.S. patent application is a Continuation-In-Part of U.S.patent application Ser. No. 10/836,482 filed Apr. 30, 2004 now U.S. Pat.No. 7,049,762 and entitled A PORTABLE FLUORESCENT TASK LAMP, whichclaims priority from earlier filed U.S. Provisional Patent Applications:Ser. No. 60/467,649 filed May 2, 2003 and entitled INTEGRATED CIRCUITFOR TASK LIGHT, and Ser. No. 60/467,981 filed May 5, 2003 and entitledELECTRICAL CIRCUIT FOR A PORTABLE FLUORESCENT TASK LAMP.

BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates generally to the field of electricallighting devices and, more specifically, to fluorescent lamps whichfeature electronic ballast circuits for the control of multiplefluorescent lamp bulbs of various types and light output ratings.

B. Description of the Prior Art

The prior art devices used for illumination in a work area have includedbattery powered flashlights that have a limited life and a narrow focus;incandescent drop-lights that feature electrically inefficient, very hotand volatile tungsten filaments; and also various types of fluorescentlights. Battery-powered flashlights typically offer less illuminationthan AC powered lights, and the batteries, even if rechargeable, are notoperable continuously without recharging or replacing the batteries.

Portable, hand-held drop lights or task lights utilizing an incandescentbulb and powered by AC line current, typically 120 Volts AC, 60 Hz,allow the user to provide light where installed light fixtures do notprovide adequate coverage. However, incandescent bulbs as the lightsource in task lamps have several disadvantages. Although incandescentlight bulbs are a well-developed technology and are economical topurchase, they are not economical to operate. Much of the electricalenergy used by the task light is converted to heat. The tungstenfilament in a typical 100 Watt incandescent bulb causes the bulb to gettoo hot to touch in many common work area situations such as a task lampbeing used by a technician to illuminate the engine compartment of anautomobile. Moreover, the relatively fragile nature of the incandescentlamp with its glass bulb and its tungsten filament presents furtherdrawbacks.

One alternative to the use of incandescent bulbs is the fluorescentbulb. Fluorescent bulbs convert more of the supplied electrical energyto light energy and operate at lower external temperatures than doincandescent lights. The light emitting medium in fluorescent lights isa phosphor coating, unlike the thin, fragile tungsten filament in anincandescent light bulb. In a fluorescent lamp bulb, a glass tubecontaining a small amount of gas—mercury vapor, for example—is providedwith coated cathode electrodes at either end of the tube. When a highenough voltage is applied between each pair of electrodes at the ends ofthe glass tube, the coated filament is heated and emits electrons intothe gas inside the tube. The gas becomes partially ionized and undergoesa phase change to a plasma state. The plasma is conductive and permitsan electric arc to be established between the electrodes. As currentflows in the plasma, electrons collide with gas molecules, boosting theelectrons to a higher energy level. This higher energy level is not astable condition and when the electron falls back to its normal energylevel, a photon of ultra-violet light is emitted. The photons in turncollide with the phosphor coating on the inside of the glass tube,imparting their energy to the phosphor ions, causing them to glow in thevisible spectrum. Thus the phosphor coating luminesces and gives off thecharacteristic “fluorescent” light.

Fluorescent bulbs, however, typically require a higher voltage toinitiate the plasma state than is required to maintain the plasma stateand the luminescence. Further, after becoming a plasma, the effectiveresistance of the plasma between the electrodes drops increasingly asthe current increases. Unless the current is limited, the tube will drawexcessive current and damage itself and/or the supply circuit. Typicalpractice to limit the current is to provide a damping circuit, called a“ballast,” that operates to ignite the gas tube while also limiting thesupply current. The ballast for full-sized installed light fixturesincludes a large transformer/inductor, to transform the supplied linevoltage, typically 120 Volts AC available at a wall outlet to a highenough potential to ignite the lamp and also to provide a high enoughinductive impedance in the supply circuit to limit the current duringoperation. For typical installed lighting fixtures usingnon-self-starting bulbs and operating at 120 VAC, 60 Hz, the wire gauge,the number of turns in the coils, and size of the magnetic core resultin a large and heavy ballast component. The ballast circuits forso-called “self-starting” fluorescent bulbs are typically smaller, yetstill provide an appropriate voltage to ignite the lamps without aseparate starter. The ballast circuit then regulates the current draw ina similar manner to that previously described for non-self startingbulbs.

Battery operated fluorescent lamps are well-known in the art but theiruse is usually limited to applications such as camp lighting oremergency lighting where a bright illumination is not essential. Batteryoperated fluorescent lamps typically cost more initially because theyrequire an extra circuit to produce a high voltage, high frequency ACsupply to operate the fluorescent bulb. Operation of the lamp at ahigher frequency enables the use of smaller components which cost lessand take up less space. Heretofore, a battery operated fluorescent tasklamp, because of the additional circuit complexity, was relatively moreexpensive than a conventional AC line-operated task lamp. Such a ballastcircuit thus can add complexity, cost, and an increased electrical loadon the battery power supply if not carefully designed.

In one example of the prior art, U.S. Pat. No. 6,534,926, Miller et al.,a portable fluorescent drop light is disclosed that contains a pair oftwin-tube compact fluorescent lamp (CFL) bulbs that are individuallyswitched. The discrete solid state drive circuit used as a ballast fornon-self-starting bulbs utilizes the CFL bulbs as part of theoscillating circuit and has a relatively high component count. Thecircuit relies on several transformers, including separate windings foreach CFL bulb, and a separate feedback protection circuit, to producethe drive voltage while limiting the current drawn by the bulbs duringthe run condition. Moreover, a different circuit is required for usewith self-starting bulbs. Miller et al. thus has the disadvantages ofrelatively high component count, use of several transformers, and is notcapable of driving non-self-starting or self-starting bulbs from thesame ballast circuit. Further, since the lamps themselves are part ofthe oscillator circuits in Miller et al., the oscillator frequency isnot independent of the variations in lamp characteristics unit-to-unit,and is thus subject to varying levels of performance.

A need exists, therefore, for an economical, portable hand-held tasklamp that provides light output equivalent to that of a 100 Wattincandescent bulb, is efficient to operate, and does not operate atexcessively high temperatures. A need also exists for a ballast circuitdesign which eliminates the need for a heavy transformer component andcan preferably work with either self-starting or non-self-startingbulbs. The lamp should be sturdy and durable and replacement bulbsshould be inexpensive, readily available, and easily changed. It wouldbe a further desirable feature to provide variable illumination and aslight-weight and compact a lamp as possible.

SUMMARY OF THE INVENTION

The present invention has as its object to overcome various of theshortcomings in the prior art described above. More specifically, it isan object of the present invention to provide a portable fluorescenttask lamp having a ballast circuit design that is very efficient andoperates with at least two “self-start” and “non-self start” typefluorescent bulbs of the type currently employed in task lamps of thedrop light variety. The ballast circuit design will also preferablyenable independent switching of twin or quad configuration, compactfluorescent light (CFL) bi-pin bulbs.

Accordingly there is disclosed a portable hand held fluorescent tasklamp, comprising: an elongated housing molded of thermoplastic materialand having a clear lens on a first side of a first end of the housingand a hand grip formed into the housing at a second end of the housing;a line cord; at least two compact fluorescent lamp (“CFL”) bulbsremovably disposed within the first end of the housing behind andvisible through the clear lens, wherein each of the CFL bulbs mayberated at any wattage from approximately four Watts to approximatelytwenty four Watts and the CFL bulbs may be either a non-starting type ora self-starting type; a transformerless electrical drive circuitdisposed within the elongated plastic housing, and connected at a firstinput to the line cord and connected at least first and second outputsto the at least two CFL bulbs, wherein the electrical drive circuit ispowered by a 120 VAC or 240 VAC line voltage provided by the line cordconnected to the first input; and an SPST switch connected in serieswith each CFL bulb, wherein each SPST switch includes an ON conditionand an OFF condition; wherein the at least two CFL bulbs are ignited andsustained in illumination in parallel, simultaneously or individually asdetermined by the respective condition of each SPST switch.

In an alternate embodiment, a transformerless electrical drive circuitconnected to drive at least first and second fluorescent bulbs having apredetermined wattage rating is provided, the transformerless circuitconnected at a first input to a common return node of a power supply andconnected via a common output node to the fluorescent bulbs; a firstseries connection between the common return node and the common outputnode including a first current limiting inductor, a first node, a firstsingle pole single throw (SPST) switch and the first fluorescent bulb;and a second series connection between the common return node and thecommon output node including a second current limiting inductor, asecond node, a second SPST switch and the second fluorescent bulb;wherein the fluorescent bulbs are ignited and sustained in illuminationin parallel as determined by a respective ON or OFF condition of eachrespective first and second SPST switches, independent of the startingcharacteristics of the fluorescent bulbs.

Additional objects, features and advantages will be apparent in thewritten description and the accompanying drawings which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a preferred embodiment of a portablefluorescent task lamp of the present invention; and

FIG. 2 is an electrical schematic of one embodiment of an electricalcircuit used in the portable fluorescent task lamp of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is shown a two-bulb, portable fluorescenttask lamp according to the present invention, designated generally as11. The task lamp 11 includes an elongated housing configured as a twopiece plastic housing 13 that may be molded of a thermoplastic material.A transparent portion of the housing is configured as a lens 15. Thelens 15, which curves approximately half-way around the front half ofthe upper portion of the housing 13, is preferably fabricated of asuitable rugged and optically clear acrylic or polycarbonate material.The housing halves 13 may be configured to accommodate circuitry withina handle portion and a pair of twin-tube CFL bulbs 19 disposed withinthe housing 13 and enclosed behind the lens 15. A reflector 17 is alsopositioned within the housing 13 and behind the twin-tube CFL bulbs 19.The reflector 17 may be fabricated of a thin, aluminum coated, heatresistant material that can be formed into a curved shape to directbackward-emitted light from the twin-tube CFL bulbs 19 in a forwarddirection through the lens 15. Each of the twin-tube, bi-pin CFL bulbs19 may be plugged into a corresponding receptacle (not shown) tofacilitate connecting the bulbs 19 to the ballast circuit (see FIG. 2).

The portable task lamp 11 may also include end caps (not shown) and ahook (not shown) attached to one or both of the end caps, which allowsthe lamp to be conveniently suspended in a work area. In the exampleshown, the lamp 11 houses two twin-tube compact fluorescent light (CFL)bi-pin bulbs 19, although other arrangements are possible. For example,present commercially available CFL bulbs are typically provided aseither a twin-tube standard bulb or a quad-tube standard bulb. Thetwin-tube types have the advantage that they are less bulky, lessexpensive and more readily available. However, the twin-tube types areof approximately half the power (13 W) and light output of the quad-tubelamps. While the quad-tube design offers approximately twice the power(27 W) and illumination of a single twin-tube, the quad-tube bulb istypically more complex to produce. It is further more expensive and isnot as readily available. In the illustrative embodiment of FIGS. 1 and2 described herein, the pair of twin-tube CFL bulbs 19 are each rated atapproximately 13 Watts and together provide the equivalent illuminationof a 100 Watt incandescent bulb drop light.

Just visible in FIG. 1, near the upper portion of the handle portion ofthe housing 13 on the rear side, is a switch actuator 21. It is one oftwo rocker switches mounted side-by-side in the location described foroperating each of the pair of twin-tube CFL bulbs 19 alone or in tandemas will be described herein below. The lamp may be powered by 120 VoltsAC supplied through power cord 23. The lamp 11 is readily adaptable toother supply voltages such as 120 Volts AC, 50 Hz or 240 Volts AC, 50/60Hz.

Referring to FIG. 2, there is illustrated a schematic diagram of oneembodiment of a ballast or drive circuit for the two-bulb, portablefluorescent lamp 11 according to the present invention. In theillustrated example shown and described, the wattage rating of thefluorescent bulbs is predetermined at 13 watts and the ballast circuitis configured accordingly. The supply mains lines L and N, 25, 27respectively, supply operating current to the circuit. The line L of thesupply mains is coupled through a 15 Ohm, 1 Watt resistor that functionsas a fuse F1 (29), to a node 32. The line N (27) of the supply mains iscoupled to a node 43, which is the common return node of the powersupply. Diodes D1 (31) and D2 (33) respectively, are connected in seriesbetween a positive supply node 35 and a negative supply node 37. Thediode rectifiers 31 and 33 are joined at node 32. 22 uFd, 250 Volt DCFilter capacitors 39 and 41 are connected in series between the supplynodes 35 and 37. The filter capacitors are joined at the node 43. Theforegoing components comprise a voltage doubler power supply forproviding an operating voltage of approximately 270 Volts DC to theremaining circuitry to be described.

Continuing with FIG. 2, the twin-tube CFL lamp bulbs, CFL1 (69) and CFL2(71) are connected in parallel lamp circuits between a supply node 59and the common node 43. Each of the CFL bulbs 69, 71 include bipinterminals A and B. The CFL bulbs 69, 71 in the illustrated embodimentare each 13 watt compact fluorescent lamps, NEMA type CFT13/G23d. Thecircuit of FIG. 2 may be readily adapted to other wattage ratings andstyles of CFL bulbs. The B terminals of the CFL bulbs 69, 71 areconnected to the supply node 59. Connected in series between the Aterminal of the CFL1 bulb 69 and the common node 43 are a SPST switch65, a node 51, and a first current limiting inductor L1 (45). Connectedin series between the A terminal of the CFL2 bulb 71 and the common node43 are a SPST switch 67, a node 53, and a second current limitinginductor L2 (47). The inductors L1 (45) and L2 (47) function as ballastchokes that limit the current that flows in each respective CFL bulbafter the CFL bulb ignites. The inductors L1 (45) and L2 (47) arespecially wound on EE25 cores that include a gap, and have an inductanceof 3.3 mH. In addition, the inductance of the inductors L1 and L2resonates with the internal capacitance (not shown) of the CFL bulbs,whether it is a non-self-starting or self-starting type of CFL bulb. Thevalue of the inductance of L1 and L2 must also take into considerationthe wattage rating of the CFL bulb being used. A pair of couplingcapacitors 55, 57, which are connected in series between nodes 51 and53, are joined at a node 49. The first 55 and second 57 couplingcapacitors, C9 (55) and C10 (57) in the illustrative embodiment, are 330pF, 1 KV ceramic capacitors. The anode of a diode rectifier D3 (61) andthe cathode of a diode rectifier D4 (63) are also connected to the node49. The cathode of the diode D3 (61) is connected to the positive supplyvoltage terminal pin 2 of IC1 (103) and the anode of the diode D4 (63)is connected to the voltage supply return terminal pin 8 of IC1 (103).Rectifier diodes D3 (61) and D4 (63) are type 1N4148 signal diodes. Thepair of SPST switches 65, 67 are part of the switch actuator 21described herein above in FIG. 1 and are used as ON/OFF switches toindependently turn ON or OFF the CFL bulbs 69, 71. The component valuesfor the first and second current limiting inductors 45, 47 and therespective first and second coupling capacitors 55, 57 may be scaled inrelation to the predetermined wattage ratings of the fluorescent bulbs69, 71.

Continuing with FIG. 2, the electrical drive circuit (an electronicballast circuit) of the illustrated embodiment will now be described.The circuit of FIG. 2 is based on an integrated circuit IC1 (103) thatdevelops output signals to drive a pair of MOSFET transistors Q1 (105)and Q2 (107) connected in series across the positive supply at node 35and the negative supply at node 37. The IC1 in the illustratedembodiment, which provides the control portion of the electrical drivecircuit, is a type IR2156 manufactured by International Rectifier, ElSegundo, Calif. 90245 USA. The MOSFET transistors in the illustratedembodiment are type IRF720 from the same manufacturer. The type IRF720is rated at 400 Volts, 3.3 Amperes and has an Rds ON of 1.8 Ohms. Aresistor R1 (73) is connected between node 35 and a node 77. A capacitorC3 (91) is connected between the node 77 and the node 37. The node 77 isalso connected to pin 3 of the IC1 (103). A resistor R2 (75) isconnected between the node 35 and a node 83, which is also connected topin 2, the Vcc supply voltage terminal of the IC1 (103). A capacitor C8(85) is connected between the node 83 and the node 37. As previouslydescribed, the cathode of diode D3 (61) is also connected to the node 83and the anode of the diode D4 (63) is connected to the node 37. As willbe described further herein below, the networks C9 (55) and D3 (61), andC10 (57) and D4 (63) are charge pump circuits for ensuring sufficientoperating voltage for the IC1 (103) under certain conditions.

Continuing with FIG. 2, the anode of a diode D5 (102) is connected tothe node 83 and the cathode of diode D5 (102) is connected to a node 81,which is connected to pin 14 of the IC1 (103). A capacitor C7 (99) isconnected between a pin 12 of the IC1 (103) and the node 81 at pin 14 ofthe IC1 (103). Pins 8 (the Vss or return supply terminal) and 9 of theIC1 (103) are connected to the node 37. A capacitor C4 (95) is connectedbetween pin 6 of the IC1 (103), which is also designated as a node 79,and the node 37. A resistor R5 (113) is connected between the node 79and a pin 4 of the IC1 (103). R5 (113) is a timing resistor and C4 (95)is a timing capacitor. Together, R5 and C4 determine the run frequencyof the oscillator in the IC1 (103). A resistor R6 (115) is alsoconnected between the node 79 and a pin 5 of the IC1 (103). Capacitor C4(95) and the resistors R5 (113) and R6 (115) set the timing values forthe oscillator within the IC1 (103). R6 and R5, when connected inparallel by a transistor mode switch (not shown) within the IC1 (103),reduce the RC time constant for the oscillator to increase theoscillator frequency during the preheat mode, as will be describedherein below.

A high side output drive signal from pin 13 of the IC1 (103) is coupledto a gate terminal of the transistor Q1 (105). A low side output drivesignal from pin 11 of the IC1 (103) is coupled to a gate terminal of thetransistor Q2 (107). The gate terminals of the transistors Q1 (105) andQ2 (107) are driven out of phase with respect to each other by the pulsewaveform of the drive signals from the IC1 (103). The repetition rate ofthe drive signals, as set by the RC time constants (see the previousdescription for R5 and R6 and C4), may be in the range of approximately30 KHz to 50 KHz in a typical application. The operating frequencies arealso influenced by the characteristics of the particular CFL bulbs usedin the circuit. For example, fluorescent bulbs include an internalcapacitance that controls the starting behavior of the bulb. The valueof this capacitance may vary as to whether the bulb is anon-self-starting or self-starting type. Thus, this capacitance is amongthe frequency determining components of the circuits.

As mentioned previously, the transistors Q1 (105) and Q2 (107) areconnected in series across the positive supply node 35 and the negativesupply node 37 to form the output stage of the electronic ballastcircuit illustrated in FIG. 2. The drain terminal of the transistor Q1(105) is connected to the node 35 and the source terminal of thetransistor Q2 (107) is connected to the node 37. The drain terminal ofthe transistor Q2 (107) and the source terminal of the transistor Q1(105) are connected together at an output node 93. The output node 93 isconnected to the node 59, which is connected to the B terminals of bothCFL lamps 69, 71. Transistors Q1 (105) and Q2 (107) form a half-bridgeMOSFET drive circuit that alternately drives both CFL bulbs 69, 71 witha high frequency AC voltage of approximately 120 Volts AC.

In operation, each twin-tube CFL bulb (69, 71) of the illustratedembodiment shown in FIG. 2 may be switched ON or OFF independentlyaccording to the condition of the SPST switches 65, 67. The inductorsL1, L2 (45, 47) set the operating power and current of the bulbs.Operating voltage for the IC1 (103) is provided to pin 2 of IC1 (103) bythe network R2 (75), node 83 and C8 (85). Voltage to operate the highside driver circuit internal to the IC1 (103), is provided by abootstrap network of D5 (102) connected to pin 14 of the IC1 (103) vianode 81, and C7 (99) connected between pins 14 and 12 of the IC1 (103).The DC voltage available at node 35 is measured by IC1 (103) at pin 3via the network R1 (73) and C3 (91) coupled to the node 77. The networksC9 (55) and D3 (61), and C10 (57) and D4 (63) are charge pump circuitsfor ensuring sufficient operating voltage for the IC1 (103) when thesecond one of the two CFL lamps 69, 71 is to be ignited. This conditionoccurs, for example, when both of the switches 65, 67 are in an ONcondition, or one of the switches 65, 67 is switched ON after the otherof the switches 65, 67. The charge pump networks also function to resetthe sweep signal generated within the IC1 (103) that controls thepreheat segment of the ignition sequence for the CFL bulbs 69, 71. Thissweep signal is adaptive in the sense that its timing automaticallyadapts to the type of CFL bulb in the circuit, i.e., whether the bulbsare non-self-starting or self-starting types.

Continuing with the operation of FIG. 2, the drive signals to the MOSFETtransistors proceed sequentially through three modes after a first oneof the switches 65, 67 is turned ON. The first mode is a preheatmode—about 8/10ths of a second—to warm up the filaments in the CFLbulb(s) as set by the preheat resistor R6 (115) and the preheatcapacitor C5 (97). The oscillator in IC1 (103) runs at a frequencydetermined by the time constant of R5 and R6 (in parallel) and C4. Whenthe voltage across the preheat capacitor C5 (97) ramps upward to andreaches a first predetermined voltage (starting from zero volts), thetransistor mode switch (not shown) within IC1 (103) disconnects thepreheat resistor R6 and causes the oscillator frequency to ramp downwardtoward the run frequency determined by the R5, C4 time constant. As theoscillator frequency ramps downward, the AC output voltage produced atthe output node 93 ramps upward to ignite the bulb(s). When the voltageacross the preheat capacitor C5 (97) continues past the firstpredetermined voltage and reaches a second, higher predeterminedvoltage, the downward change of the oscillator frequency is halted, theCFL bulb(s) ignites because of the higher voltage impressed across thebulb(s), and the oscillator begins to operate at the run frequency setby the RC time constant of R5 and C4. The brief period during which theoscillator frequency ramps downward toward the run frequency is calledthe ignition ramp mode of operation. After the bulb(s) ignite, thecircuit enters the run mode wherein the output voltage at output node 93stabilizes at approximately the same level as during the preheat mode.This level is maintained by the voltage developed across the currentsense resistor R4 (111), a 0.56 Ohm, 0.5 Watt resistor, and applied viathe RC network of R3 (109) and C6 (101) to pin 10 of IC1 (103).

The foregoing is a summary of the operation of the electronic ballastcircuit of FIG. 2. Further details of the operation of the integratedcircuit IC1 (103) may be found in International Rectifier Data Sheet No.PD60182-I for the Ballast Control IC, type IR2156(S), which isincorporated herein by reference in its entirety. This ballast controlintegrated circuit is designed to drive a single, non-self-starting,compact fluorescent lamp (CFL) bulb. The wattage rating of the CFL bulbthat is chosen may be accommodated by selecting appropriately ratedMOSFET output transistors and adjusting other component valuesaccordingly, as is well within the capability of persons skilled in theart. In the present invention, however, a way is demonstrated to drivetwo non-self-starting OR self-starting CFL bulbs, together orindependently, using a single ballast control circuit. Althoughapparently simple, the modifications necessary to ensure firing of bothbulbs, together or in sequence—by providing carefully selected ballastchoke (inductors 45, 47) values, and a charge pump network for each CFLbulb 69, 71 that also participates in resetting the preheat sequence forthe second bulb—is not previously known. Values for the first and secondcurrent limiting inductors 45, 47 and the respective first and secondcoupling capacitors 55, 57 maybe scaled in relation to the wattageratings of the fluorescent bulbs 69, 71.

A number of advantages are readily apparent in the circuit design ofFIG. 2. The use of the integrated circuit and half-bridge architecturein the circuit design of the invention minimizes the number and size ofthe inducive devices, and allows a reduction in the overall number ofrequired components and a consequent reduction in cost and circuit boardspace requirements. Further, the configuration provided by the presentinvention enables the same minimum-parts design to be used with avariety of twin-CFL bulb ratings simply by adjusting the values ofseveral components that affect the current levels, frequencies and thetiming sequence of the three modes of operation. In the illustrativeexample shown, two 13 watt CFL bulbs provide illumination that isapproximately equivalent to a 100 watt incandescent bulb in a portabletask light that uses much less energy and is much cooler in operation.An addition of two diodes (e.g., type IN7007) across a second line L2 toform a full-wave bridge rectifier (not shown, but readily understood bythose skilled in the art) allows an easy conversion from the voltagedoubler power supply to accommodate the 120 VAC or the full-wave bridgeto accommodate the 240 VAC input power. Moreover, the circuit of FIG. 2works with either non-self-starting or self-starting bulbs because ofthe characteristics of the ballast control IC and the particularselection of component values in the charge pump/current limitingnetworks for each of the CFL bulbs.

While the invention has been shown in only one of its forms, it is notthus limited but is susceptible to various changes and modificationswithout departing from the spirit thereof. For example, other BallastControl integrated circuits designed for use with a single CFL bulb maybe used in a circuit adapted for two or more CFL bulbs according to theprinciples of the present invention, i.e., providing for a charge pumpcircuit that operates independently with either bulb. The separate SPSTswitches may be replaced with other configurations, either manuallyoperated switches or remotely-actuated electronic switches or automaticswitches controlled by illumination levels, and the like, for thecontrol of the individual lamp elements.

The same circuit as illustrated herein may be adapted to any of numerousconfigurations and wattage ratings and light output requirements merelyby selecting appropriate component values as previously described. Insome configurations, for example, the CFL bulbs may be of mixed type andwattage ratings, requiring only the careful selection of componentvalues in the lamp circuits such as the charge pump and current limitingnetworks. In other configurations, the circuit described in FIG. 2, withcomponent values accordingly scaled to the power requirements of thefluorescent bulbs, may be used with fluorescent bulbs other than thecompact fluorescent (“CFL”) type. For example, a ballast circuit for apair of standard fluorescent bulbs (not shown) having a predeterminedwattage rating may be readily based on the ballast circuit of FIG. 2with scaled values for the current limiting inductors, couplingcapacitors and semiconductor ratings, without departing from theprinciples of the present invention disclosed herein. Moreover, thepower supply may be adapted to operate from any world-wide AC mainsstandard. Rechargeable versions of the portable fluorescent lampdisclosed herein may be provided by replacing the AC input power supplywith a DC-operated inverter circuit and rectifier to provide the highvoltage DC to operate the high frequency drive circuit.

1. An electrical drive circuit for starting and running fluorescentbulbs, comprising; a transformerless electrical drive circuit connectedat a first input to a common return node of a power supply connected toa line cord and connected via a common output node to at least first andsecond fluorescent bulbs having a predetermined wattage rating; a firstseries connection between the common return node and the common outputnode including a first current limiting inductor, a first node, a firstsingle pole single throw (SPST) switch and the first fluorescent bulb;and a second series connection between the common return node and thecommon output node including a second current limiting inductor, asecond node, a second SPST switch and the second fluorescent bulb;wherein the at least first and second fluorescent bulbs are ignited andsustained in illumination in parallel as determined by a respective ONor OFF condition of each respective first and second SPST switches,independent of the starting characteristics of the first and the secondfluorescent bulbs.
 2. The apparatus of claim 1, wherein thetransformerless electrical drive circuit includes a charge pump networkfor enabling the ignition and continuous illumination of each of the atleast first and second fluorescent bulbs.
 3. The apparatus of claim 2,wherein the charge pump network comprises: first and second reversebiased diodes connected in series between a positive terminal and anegative terminal of a control portion of the electrical drive circuit,wherein a third node is defined at a junction between the first andsecond diodes; a first coupling capacitor connected between the firstnode and the third node; and a second coupling capacitor connectedbetween the second node and the third node.
 4. The apparatus of claim 3,wherein the values of the first and second coupling capacitors arescalable in relation to the wattage rating of the respective fluorescentbulbs.
 5. The apparatus of claim 1, wherein each of the at least firstand second fluorescent bulbs include a wattage rating of up to fortywatts.
 6. The apparatus of claim 1, wherein the values of the first andsecond current limiting inductors are scalable in relation to thewattage rating of the respective fluorescent bulbs.
 7. The apparatus ofclaim 1, wherein the transformerless electrical drive circuit providesfor preheat, ignition, and run modes of operation of the at least firstand second fluorescent bulbs.
 8. The apparatus of claim 1, wherein thetransformerless electrical drive circuit further comprises: a controlcircuit having a Vcc terminal connected to a positive supply voltage, aVss terminal connected to the common return node and having preheat,ignition, and run modes of operation of the at least first and secondfluorescent bulbs.
 9. The apparatus of claim 1, wherein thetransformerless electrical drive circuit is powered by a 120 VAC or 240VAC line voltage provided by the line cord connected to the powersupply.
 10. An electrical drive circuit for a fluorescent lamp,comprising: a transformerless circuit, connected to drive at least firstand second fluorescent bulbs having a predetermined wattage rating, thetransformerless circuit connected at a first input to a common returnnode of a power supply connected to a line cord and connected via acommon output node to the at least first and second fluorescent bulbs; afirst series connection between the common return node and the commonoutput node including a first current limiting inductor, a first node, afirst single pole single throw (SPST) switch and the first fluorescentbulb; and a second series connection between the common return node andthe common output node including a second current limiting inductor, asecond node, a second SPST switch and the second fluorescent bulb;wherein the at least first and second fluorescent bulbs are ignited andsustained in illumination in parallel as determined by a respective ONor OFF condition of each respective first and second SPST switches,independent of the starting characteristics of the first and the secondfluorescent bulbs.
 11. The electrical drive circuit of claim 10, whereinthe transformerless electrical drive circuit includes a charge pumpnetwork for enabling the ignition and continuous illumination of each ofthe at least first and second fluorescent bulbs.
 12. The apparatus ofclaim 11, wherein the charge pump network comprises: first and secondreverse biased diodes connected in series between a positive terminaland a negative terminal of a control portion of the electrical drivecircuit, wherein a third node is defined at a junction between the firstand second diodes; a first coupling capacitor connected between thefirst node and the third node; and a second coupling capacitor connectedbetween the second node and the third node.
 13. The apparatus of claim12, wherein the values of the first and second coupling capacitors arescalable in relation to the wattage rating of the respective fluorescentbulbs.
 14. The apparatus of claim 10, wherein each of the at least firstand second fluorescent bulbs include a wattage rating of up to fortywatts.
 15. The apparatus of claim 10, wherein the values of the firstand second current limiting inductors are scalable in relation to thewattage rating of the respective fluorescent bulbs.
 16. The apparatus ofclaim 10, wherein the transformerless electrical drive circuit providesfor preheat, ignition, and run modes of operation of the at least firstand second fluorescent bulbs.
 17. The apparatus of claim 10, wherein thetransformerless electrical drive circuit further comprises: a controlcircuit having a Vcc terminal connected to a positive supply voltage, aVss terminal connected to a supply voltage return and preheat, ignition,and run modes of operation of the at least first and second fluorescentbulbs.
 18. The apparatus of claim 10, wherein the transformerlesselectrical drive circuit is powered by a 120 VAC or 240 VAC line voltageprovided by the line cord connected to the power supply.